Power-line communication (“PLC”) is a term used to describe the transmission and reception of data on conductors that are also used simultaneously for AC electric power distribution. Technical problems associated with PLC technologies include recovering the received signal in the presence of narrowband interference and impulse noise. A PLC system operating in an industrial environment may, for example, contend with narrowband noise induced into the conductors by industrial equipment such as welding machines.
FIG. 1 is a prior-art block diagram of a PLC system 100. A master node 105 includes a transmitter 107 to transmit packets to a receiver 109 in a slave node 110 across a downlink path 115. A transmitter 117 in the slave node 110 transmits packets to a receiver 119 in the master node 105 across an uplink path 120. Modern PLC systems are typically packet-based, operate in half-duplex mode, and transmit an orthogonal frequency division multiplexed (“OFDM”) modulated carrier signal across two conductors of a power wiring circuit. Thus, the downlink path 115 and the uplink path 120 are typically implemented across the same two conductors in half-duplex mode and are generally distinguished as logical rather than physical paths. It is also noted that the terms “downlink” and “uplink” as used herein are arbitrarily chosen to refer to master-to-slave and slave-to-master packet traversal paths, respectively.
Various PLC standards specify various frequency bands, data rates and distance limits. Since the power distribution system is intended for transmission of AC power at typical frequencies of 50 or 60 Hz, power circuits have only a limited ability to carry higher frequencies. Low-frequency (100-200 kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second. Such PLC channels may extend several miles. Higher data rates generally imply shorter ranges. For example, a PLC-implemented local area network operating at megabits per second may only cover one floor of an office building.
Narrowband PLC standards specify various frequency bands including the European Committee for Electrotechnical Standardization (“CENELEC”) Band A (35 kHz-91 kHz), CENELEC Band B (98 kHz-122 kHz), the Association of Radio Industries and Businesses (“ARIB”) band (154 kHz-403 kHz) and the Federal Communications Commission (“FCC”) band (155 kHz-487 kHz). Other standards such as G3, IEEE1901.2 and PRIME specify characteristics of the physical layer, including numbers of sub-carriers associated with the OFDM PLC signal. The magnitudes of spectral components of interference overlapping a PLC signal may vary dynamically with time as rotating machinery, welding equipment, electronic power supplies and other sources of interference are powered up and shut down.